位于巨型走滑断裂端部盆地演化的地质模型——以苏丹穆格莱德盆地为例

横跨非洲大陆中部巨型中非断裂带东端的穆格莱德盆地的演化与周邻的大地构造背景密切相关。在早白垩世的演化与大西洋的分阶段张裂密切相关,晚白垩世的演化与印度块体的快速北移有关,新生代的演化主要和红海的扩张有关。盆地的构造演化可划分三大阶段:在早白垩世盆地发育的鼎盛时期,受中非走滑断裂的影响,盆地沉降速率巨大,沉积中心和沉降中心往往不一致;在晚白垩世,盆地为断陷和坳陷型沉积,沉积中心向远离中非断裂带的东南方向迁移。盆地总体的演化具有从走滑型向拉张伸展型转化的特点。在盆地演化的早期,烃源岩和储集岩在靠近中非走滑断裂带附近较发育;在晚期的构造挤压作用下,一方面对已形成的油气藏进行破坏,同时,可造成油气重新分布,形成一些新生的油气藏。在该部位沉降中心和沉积中心往往不一致,这给油气的勘探带来新的困难,因此对这些地区的勘探要十分慎重。在远离中非断裂带的盆地东南部,是晚期沉积和沉降的中心,主力烃源岩演化比较适中,油气成藏期较晚,是寻找具有工业价值油气田的有利部位。

GEOLOGICAL MODEL OF THE MUGLAND BASIN-AN IDENTICAL EXAMPLE OF BASIN EVOLUTION AT THE END OF GIANT STRIKE-SLIP FAULTS

The basin evolution at the end of giant Central African strike slip fault is closely related to the regional tectonic background. Evolution of the basin in the Early Cretaceous resulted from the seperation of Atlatic Ocean, and that in the Later Cretaceous from the northward movement of the India plate . The spreading of Red Sea in the Cenozoic have also influenced the evolution of the basin. Three stages of the structural evolution for the basin can be classified: Early Cretaceous, Late Cretaceous and Cenozoic. In the Early Cretaceous, owing to activity of the central African strike slip fault, the subsidence speed was enormous, in which the depositional and subsiding centers were not in the same position. In the Late Cretaceous, the basin was dominated by both rifting and sag, and the depositional center moved towards the southeast of the basin where was far away from the central African fault. In general scene, the structural evolution for the basin was transformed from the strike slip to the extensional system. Potential source rocks and reservoirs were developed along the central African fault in the early evolution of the basin. Under the structural compression in the late stage, some oil and gas pools could be destroyed, and resulted in hydrocarbon redistribution and formation of new accumulations. The difference in depositional and subsiding centers brought out the difficulty in exploration. In the southeast of the basin far away from the central African fault, the main source rocks were matured properly, and depositional and subsiding centers were in the same place, so many industrial oil and gas fields have been found.